This revised application addresses hypotheses developed from work that the investigators carried out in the initial UCLA Epilepsy Surgery Program concerning the extent and nature of functional plasticity in young children following early hemispherectomies. The proposed project addresses key questions concerning the capacity of the human brain for functional plasticity. The investigators will test hypotheses about the functional plasticity of language, certain cognitive functions, and social communication in a unique cohort of children who have received left or right hemispherectomies for medially intractable epilepsy prior to 10 years of age. They will attempt to better define the temporal "window" for functional plasticity. They will determine if age at seizure onset and age at surgery predict the extent to which children show functional plasticity for specific linguistic, cognitive, and social communication function. The effect of seizure etiology on functional plasticity will be examined by comparing 1) children with and without evidence of cortical dysphasia in the resected hemisphere and 2) children with Rasmussen encephalitis to children with cerebral infarcts within the non-cortical dysplasia groups. This project represents a singular opportunity to more fully integrate the work conducted in their respective laboratories in order to examine the interrelation between language, cognition, and social communication in the isolated right and left hemispheres of children receiving early hemispherectomies. These questions will be addressed at two, five and ten years of age in the UCLA Pediatric Epilepsy Surgery Program. The investigators are currently following almost 50 children starting from pre-surgical evaluation to follow-up intervals ranging from 1 to 12 years. During the follow-up evaluations, children will be administered a careful selected set of tasks which have been demonstrated in prior research to tap linguistic, cognitive and social communication function normally lateralized to either the left or right hemisphere. This will provide the investigators the opportunity to determine the extent to which an isolated left or right hemisphere can support functions normally supported by the resected hemisphere.